岷江断裂带晚新生代逆冲推覆构造:来自钻孔的证据

Late Cenozoic Thrust and Nappe Structure along the Minjiang Upstream: Evidence from a Drill Hole

岷江断裂带由2个不同性质的断裂组成:早期岷江逆冲断裂和晚期岷江正断裂。野外地质调查和钻孔资料发现在岷江西侧山麓之下存在一套厚度大于110m的早更新世灰黑色湖相地层,三叠系灰岩逆掩在这套湖相地层之上。由此确定岷江断裂是一条西倾的逆冲断层,逆冲作用发生在中更新世之前。在中更新世时期,岷江逆冲断裂发生构造负反转,在其前缘形成一条东倾的正断层,它控制了岷江上游漳腊盆地的发育。本文认为,岷山地区现今地震活动并非受控于岷江断裂带,而可能受到虎牙断裂及岷山隆起深部滑脱构造的控制,岷江断裂带位于该深部滑脱构造的上部。进而认为逆冲—推覆构造样式可能是青藏高原东缘晚新生代造山和快速隆升的主要变形机制。

The Minjiang fault zone consists of two faults with different property ： an early thrust fault and a late normal fault. Field survey found that remnants of lacustrine deposits possibly aged Early Pleistocene, develop along the western side of the Minjiang Upstream, western Siehuan. A hole drilled at the site of Zhayigou, Gami temple, west Minjiang River, revealed that this sequence, about 110m thick, is underthrust below the Triassic carbonates. Thus, The Minjiang thrust fault corresponds, in fact, to a west-dipping fault active before the Middle Pleistocene. This thrust fault was inversed during the Middle Pleistocene and a normal fault formed at its eastern front, which controlled the development of the Zhangla basin. We consider that the seismicity across the Minshan （Minshan Mountains） uplift seems to be not controlled by the Minjiang fault, but by the geometry of a deep d6collement zone beneath the Minshan uplift. Such a thrust style may be the main deformation mechanism for late Cenozoic mountain building and fast uplift of the eastern margin of the Tibetan Plateau.